1. Field of the Invention
This invention relates to an image position adjusting apparatus for adjusting the positions of a plurality of images such that the plurality of the images may overlap one upon another. This invention also relates to a method for using the image position adjusting apparatus.
2. Description of the Prior Art
Techniques for reading out a recorded radiation image in order to obtain an image signal, carrying out appropriate image processing on the image signal, and then reproducing a visible image by use of the processed image signal have heretofore been known in various fields. For example, as disclosed in Japanese Patent Publication No. 61(1986)-5193, an X-ray image is recorded on an X-ray film having a small gamma value chosen according to the type of image processing to be carried out, the X-ray image is read out from the X-ray film and converted into an electric signal, and the electric signal (image signal) is processed and then used for reproducing the X-ray image as a visible image on a photocopy, or the like. In this manner, a visible image having good image quality with high contrast, high sharpness, high graininess, or the like, can be reproduced.
Also, when certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays, such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then scanned with stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then used during the reproduction of the radiation image of the object as a visible image on a recording material, such as photographic film, on a display device, such as a cathode ray tube (CRT) display device, or the like.
Radiation image recording and reproducing systems which use stimulable phosphor sheets are advantageous over conventional radiography using silver halide photographic materials, in that images can be recorded even when the energy intensity of the radiation to which the stimulable phosphor sheet is exposed varies over a wide range. More specifically, since the amount of light which the stimulable phosphor sheet emits when being stimulated varies over a wide range and is proportional to the amount of energy stored thereon during its exposure to the radiation, it is possible to obtain an image having a desirable density regardless of the energy intensity of the radiation to which the stimulable phosphor sheet was exposed. In order for the desired image density to be obtained, an appropriate read-out gain is set when the emitted light is being detected and converted into an electric signal (image signal) to be used in the reproduction of a visible image on a recording material, such as photographic film, or on a display device, such as a CRT display device.
Bioimage analyzers are often used in order to carry out image analyses, or the like, by viewing radiation images of objects which have been obtained from stimulable phosphor sheets.
The bioimage analyzers are used in order to carry out image analyses, such as autoradiography on RNA, proteins, or the like, X-ray diffraction methods for analyzing protein structures, or the like, and drug metabolic analyses on animals and plants. If stimulable phosphor sheets are used for the bioimage analyzers, the aforesaid image analyses, and the like, can be carried accurately and quickly.
The bioimage analyzers may also be used in order to carry out drug metabolic analyses on brains of rats by displaying radiation images of brain slices of rats. In such cases, a plurality of brain slices, which have been immersed in drugs containing a radioisotope, are adhered to a stimulable phosphor sheet, and the stimulable phosphor sheet is thereby subjected to contact exposure to radiation, which is radiated out of the brain slices. The images of the brain slices which have been stored on the stimulable phosphor sheet, are read out. The images which have thus been read out are then compared with one another and, for example, differences in metabolism for different drugs are analyzed.
In such drug metabolic analyses on brain slices, superposition processing techniques, such as subtraction processing techniques or addition processing techniques, are often carried out on image signals representing a plurality of images to be compared with one another such that an image signal representing an image more suitable for analyses may be obtained.
With the subtraction processing techniques, an image is obtained which corresponds to a difference between a plurality of radiation images of an object recorded under different conditions. Specifically, a plurality of the radiation images recorded under different conditions are read out at predetermined sampling intervals, and a plurality of image signals thus detected are converted into digital image signals which represent the radiation images. The image signal components of the digital image signals which represent the image information recorded at corresponding sampling points in the radiation images are then subtracted from each other. A difference signal is thereby obtained which represents the image of a specific structure or part of the object represented by the radiation images.
With the addition processing techniques, the image signal components of the digital image signals which represent the image information recorded at corresponding sampling points in the radiation images are added to each other. Various kinds of noise in the image signals representing the radiation images are thereby decreased, and a signal is obtained which represents an image more suitable for analyses.
In order for the superposition processing techniques, such as the subtraction processing techniques, to be carried out, it is necessary to adjust the positions of the respective images such that the plurality of the images may overlap one upon another.
However, in cases where the drug metabolic analyses are carried out on brain slices of rats, brain slice images to be compared with one another are not necessarily obtained from the same brain slice. Therefore, the sizes and reference points of these images do not completely coincide with one another. Also, when the brain slices are adhered to the stimulable phosphor sheet, the brain slices become distorted. Additionally, the brain slices become enlarged or reduced due to drugs. Therefore, even if the brain slices are obtained from the same slicing plane, radiation images completely coinciding in sizes and shapes could not be obtained. For these reasons, during comparison and analyses of images of brain slices or images of animals or plants, it was difficult to adjust the positions of the images to be compared with one another such that the images might overlap one upon another.
Accordingly, various methods for adjusting the positions of images have been proposed. For example, in U.S. Pat. No. 4,710,875, a method has been proposed wherein images of markers are recorded together with each of radiation images of an object, and the positions of the images are adjusted with reference to the images of the markers. A method has also been proposed wherein the positions of images are adjusted by manually feeding parameters, which are necessary for the position adjustment, from a keyboard. Additionally, a method has been proposed wherein a plurality of arbitrary points are designated on radiation images, and parameters for carrying out the position adjustment are thereby determined.
However, with the method wherein markers are used, when images of an object are recorded, the markers must be located at positions such that the images of the markers may not become obstructions to the images of the object. Finding such a location is difficult for the operator who carries out the image recording operations.
With the method wherein the parameters necessary for the position adjustment are manually fed from the keyboard, the operator must input values of the parameters from the keyboard. This work is also difficult.
The method wherein a plurality of arbitrary points are designated on radiation images, and parameters for carrying out the position adjustment are thereby determined has the drawbacks described below. Specifically, for example, radiation images of brain slices, and the like, are very complicated. Therefore, when position adjustment has been carried out, it is very difficult to confirm whether or not the positions of the images have been adjusted accurately.